Viral structure, taxonomy, and diagnostics

lectures 1-2

What two structures must viruses have?

nucleic acid and capsid

What kinds of genomic makeups can viruses have?

DNA or RNA, double strand or single strand

What is the term for the viral genome and protein coat all together?

nucleocapsid

What is a virion?

the entire virus particle, including nucleic acid, capsid, envelope, and surface antigens

What are the three kinds of viral morphology?

1. helical

2. icosahedral (20 triangle sides)

3. complex

How were viruses originally classified?

by the disease they caused

How are viruses classified now?

by family, subfamily, genera, and species based on the genome type/strands

Viruses are obligate __________ _________.

intracellular parasites

When is viral shedding greatest?

early in infection

When should a sample for a viral infection be taken?

within 3 days after symptom onset

What are some specimens that are acceptable for viral collection?

1. non sterile

2. sterile

3. aspirated secretions (preferred)

What material must swabs be made out of for viral collection?

dacron and rayon

If collecting a swab or tissue sample, what kind of transport mediums can be used?

viral transport medium, saline, trypticase soy broth

When should viral specimens be processed?

ASAP

If a viral specimen is not processed after 4 days, what should happen and at what temperature?

freeze the specimen at -70 C

What are the three major methods to diagnose viral infections?

1. direct detection in the specimen

2. isolation in cell culture

3. serologic assays for antibodies

Though we cannot see most viruses using brightfield microscopy, we can use it to see infected cells. What phenomenon is seen in virally infected cells?

cytopathic effect

What is the cytopathic effect?

Where infected cells swell, round, contain vacuoles, are multinucleated (syncytia), and clump together

What other ways can we directly detect viruses?

nucleic acids and antigen detection

Which of the viral diagnosis methods is considered the gold standard?

isolation of viruses in culture

What is a primary cell culture?

When a tissue is removed from an animal and processed, seeded onto a surface to form a monolayer

In primary cell lines, how many passages can occur?

a few times

In diploid cell lines, how many passages can occur?

50

What are some examples of diploid cell lines?

WI-38, MRC-5, IMR-90

What are some examples of primary cell lines?

human, rabbit, monkey kidney cells

How many times can continuous cell lines be passaged?

infinite

What kinds of cells are used in continuous cell lines?

malignant tissue cells (A549, Hep2, HeLa), vero non-human primate cells

What is the advantage to using shell vial cultures over traditional cell culture?

cells are grown on a coverslip and centrifuged, and can be read after 24-48 hours

A four fold rise in titer indicates what for diagnosis?

recent or current infection

Antivirals are _______ to the virus and target a ________ mechanism.

specific, specific

What kinds of mechanisms can be targeted using antivirals?

nucleoside incorporation, RTase, DNApol